Feline coronavirus (FCoV) is a virus that is infectious to cats all around the world. It is of positive-stranded RNA type and is part of the Alphacoronavirus 1 species of the Alphacoronavirus genus, under the Coronaviridae family.

Alphacoronavirus 1 is a species group, to which the canine coronavirus (CCoV) belongs as well as the porcine transmissible gastroenteritis coronavirus (TGEV). The feline coronavirus has two forms: the feline enteric coronavirus (FECV) infects the intestines and the feline infectious peritonitis virus (FIPV) causes the FIP (feline infectious peritonitis). Healthy cats typically shed feces containing feline coronavirus. The virus is then transmitted to other cats via fecal-oral route. The virus is transmitted in a higher rate in an environment with multiple cats more than that with single cat. In the beginning, the virus is much less benign until it mutates from FECV to FIPV. The resulting condition from this infection, the Feline Infectious Peritonitis, is fatal and has no known cure while the treatment for it is given based on outward, observable symptoms and is generally palliative in its nature.

The mature gastrointestinal epithelial cells are infected by feline enteric coronavirus (FECV). This infection has very little outward signs and is typically chronic. The virus is shed in the feces and is detectable by polymerase chain reaction (PCR) of the feces. Some cats are naturally resistant to the virus, which can prevent infection and perhaps turn said cat into a carrier. FECV mutates into feline infectious peritonitis virus (FIPV) when a virus that is infecting an enterocyte undergoes random errors.

During their natural, pre-domestication state, cats are solitary. They do not share any kind of spaces with one another so the spread of infection is minimal. Epidemiological risk of mutation is in much higher rate within domestic cats living in a group. After mutating, the FCoV obtains a tropism for macrophages while they lose their intestinal tropism. When macrophages are infected by FIPV, a fatal granulomatous vasculitis, which then develops into Feline Infectious Peritonitis, is developed.

Feline infectious peritonitis is developed depending on two factors: the mutation of the virus and low immunity. Virus mutation, in turn, depends on the rate at which FECV mutates to FIPV. Meanwhile, the immune status depends greatly on the age of the host cat, the genetic makeups, and the level of stress. The virus can be slowed down more effectively when the host cat has a higher rate of immune status.